Lithographic imaging systems are well known in the prior art for recording images. To do this, a resist coated substrate is provided and then exposed. After exposure, the resist is developed, and then the substrate is etched via a chemical and/or physical process to yield the reticulated substrate. For infrared (IR) systems, the substrate that is used is often made from a combination of Mercury, Cadmium and Telluride materials (HgCdTe). After exposure, the resist is developed and an Electron Cyclotron Resonance (ECR) method in an argon/hydrogen gas environment is used to etch the HgCdTe substrate.
For IR imaging systems, the clarity of the imaged object is, at least in part, dependent on the reticulation properties of the recording substrate, or the ability of the substrate to be sub-divided into a grid of substrate pixels during the etching process. Substrates having more pixels per unit area yield images with greater resolution than substrates with fewer pixels per unit area. It is also very desirable that the trenches are as deep and have as high a aspect ratio (ratio of depth to width) as is feasible, in order to more clearly define the pixels.
The ECR etching process mentioned above etches the trenches in the substrate to define the pixels. Accordingly, to generate IR images having increased resolution, it is desirable to slow down the ECR etching of the pixel regions to thereby enhance the reticulation of the HgCdTe substrate. This is accomplished by overlaying the pixel regions of the substrate with a thin photoresist material. Effective photoresist materials slow the etching rate of the pixel regions, which allows for greater reticulation of the HgCdTe substrate, which further allows for more pixels defined by deeper trenches and IR images of increased resolution.
Cyclical Carbon compounds such as fullerene can be added to the photoresist material to further slow the etching process and thereby enhance reticulation of the substrate. However, the addition of fullerene to the photoresist creates other difficulties in the imaging process. Specifically, fullerene is not soluble in the casting solvent of most commercially available most photoresist materials. Also, adding fullerene to most commercially available photoresist materials negatively affects the photoresist ability to accurately record an image. This, obviously, is an unwanted side effect. What is desired is a microlithography method that incorporates fullerenes into the photoresist materials to slow the photoresist etching process in a manner, but which also avoids the disadvantages of using fullerenes known in the prior art.
In light of the above, it is an object of the present invention to provide a microlithography imaging method that improves the reticulation properties of the imaging substrate. It is another object of the present invention to provide a microlithography imaging method that yields images with increased resolution. Another object of the present invention is to provide a microlithography imaging method that incorporates a fullerene material into a photoresist material to thereby enhance the ECR etching process for an HgCdTe substrate. Yet another object of the present invention is to provide a microlithography method that incorporates a fullerene material into the photoresist material via a developing solvent to slow the photoresist etching and thereby yield IR images of greater resolution. It is another object of the present invention to provide a microlithography method that is relatively easy to accomplish in a cost-effective manner.